The present invention relates generally to a dual band linear antenna developed from the concepts of J-type antenna and array-type antenna to provide dual band wireless communication, and more particularly, to a linear dipole antenna array.
The popularity of portable electric products has speeded up the development of wireless communication technique in recent years. The wireless communication device normally requires two bands to perform signal transmission and reception. For example, for the very popular wireless local area network (WLAND), according to the specification of IEEE 802.11a, b and g, the band width of the communication frequency between the access point (AP) and the WLAND card ranges at 2.4-2.5 GHz and 4.9-5.8 GHz. Therefore, a dual band antenna has to be used for the dual band device to provide the optimal effect.
In the aforementioned wireless local area network, an internal antenna is often adapted to minimize the size and provides aesthetic effect of the WLAN card, while an external antenna is typically used for the access point. FIG. 1 shows a dual band antenna commonly used in the access point. As shown in FIG. 1, a linear copper foil A1 is placed on a printed circuit board A to form a radiator, so as to form a planar antenna. However, such planar antenna has higher directivity. That is, a fan-shaped area outlined by two sides of planar orthogonal line has better transmission and reception, while the reception and transmission are poorer along the extension of the plane (that is, the area parallel to the plane). Further, being blocked by the material of the board, the radiation of the rear surface of the circuit board that does not have the copper foil is affected. Other approaches such as adhering two such planar antennas together, or placing copper foil on both sides of the circuit board to form two set of planar antennas is also proposed to improve reception and transmission of electric wave radiation. None of these approaches provides a 360° omni-directional radiation. Therefore, the improvement of radiation along the area parallel to the circuit board is still insignificant. A dead angle still exits for reception and transmission of electric wave.